1. Field of the Invention
The present invention refers to a steam pressure container with a safety lid, particularly a boiler of a steam pressure coffee machine. The container comprises an inlet opening for filling water into the container. The inlet opening is surrounded by a flange member. Further, the container has means for heating the water contained therein.
A lid member is adapted to be mounted on the flange member, whereby the lid member and the flange member have cooperating means for bringing the lid member from an open position to a sealing position and vice versa by rotation thereof around the central axis of the flange member.
Means are provided for locking the lid member in the sealing position, said means being effective as soon as the pressure in the interior of the container is greater than the ambient pressure.
Such steam pressure containers are often used in the widely known coffee brewing machines. The container is filled with water through the inlet opening and then sealed by means of the lid member before the water contained therein is heated. Usually, the container is provided with a screw-on lid member. Furthermore, an outlet conduit provided with a pressure control valve is connected to the container; as soon as a predetermined pressure is built up in the interior of the container, the heated water can escape from the container through the outlet conduit to a coffee brewing device.
In operation, considerable pressures are built up in the interior of the container. Thus, measures have to be taken that the lid member cannot be released or removed as long as there is a high pressure in the interior of the container. If in such a case the lid member would be released in an attempt to remove it, e.g. in order to refill the container with fresh water, there would be the danger that suddenly steam or hot water escapes from the container as soon as the lid member is released, with the result that the operator could be scalded.
2. Prior Art
In the British Patent No. 2,170,995 a steam pressure container having a safety lid is disclosed. The safety mechanism of this device comprises locking grooves provided in the free lower edge of the screw-on lid member and, adjacent to the flange on which the lid member is screwed-on, a piston-cylinder-assembly. The piston thereof communicates with the interior of the container and is kept in a rest position in which the lid member can be rotated by means of a spring. As soon as a certain pressure has built up in the interior of the container, the piston is displaced, against the force of the spring, such that an axially displaceable pin connected to the piston is moved towards the lid member and engages the locking grooves in the lower edge of the lid member. Thereby, the lid member is reliably prevented from being removed from the container as long as the interior of the container is pressurized, but the safety mechanism disclosed in said British Patent is not only complicated and expensive in manufacturing, but also failure-prone because the piston in the cylinder easily can be jammed, particularly if calciferous water is used.
A similar solution is disclosed in German Utility Model No. 88 02 277. The danger of a malfunction of the piston due to the calciferous water is to be eliminated by the provision of a bellows enclosing the piston-cylinder-assembly. Besides that, the design and operation of that safety mechanism is the same. However, also that mechanism is complicated and expensive in manufacturing. A further disadvantage is that the bellows is subjected to high thermal and mechanical strain resulting in a quick aging and early damage of the bellows.